The subject matter disclosed herein relates to radiation shielding and, more particularly, to a radiation shielding system for an x-ray detector (e.g., a digital detector array (DDA)).
X-ray detectors, such as digital detector arrays (DDAs), can be used in a variety of applications, including medical and industrial applications. Some components of x-ray detectors, such as the scintillator, photodiodes, and control and readout electronics, can be susceptible to radiation damage and, without radiation protection, are typically the first DDA components to fail, especially at the radiation power levels used for industrial inspection applications. When the critical components experience x-ray or gamma-ray radiation damage, the x-ray imager can become unusable. The radiation includes both internal, e.g., fluorescence, and external, e.g., direct beam, sources of radiation. External sources of radiation can be the most intense and energetic.
X-ray detectors can include radiation shielding designed to protect the electrical components of the x-ray detectors from the external radiation experienced by the x-ray imager. As illustrated in FIG. 1, in an x-ray DDA 100, the radiation shield 106 can be placed between the motherboard 102 and the imager panel 110. The radiation shield 106 can be in the form of a sheet of material with sufficient thickness to reduce the intensity of the external radiation supported by a panel support 104. This conventional radiation shield 106 is may be a flat, uniformly thick sheet of a high x-ray absorption coefficient material such as lead, tungsten, or modern pewter. This material is positioned between the section of the x-ray detector that converts x-rays to electrical signals and the control/readout electronics of the x-ray detector.
In medical applications for instance, with radiation energies below 120 keV, this conventional radiation shielding can be sufficient to protect against external and internal sources of radiation. However, with the higher radiation energies above 160 keV that can be used in industrial applications, this radiation shielding system can be insufficient. In industrial applications, when the higher energy radiation interacts with the typical shielding material, very intense low energy, e.g., about 60-80 keV, radiation can be produced via a photoelectric effect or fluorescence.
Fluorescence emits directionally 360° and can be produced by the very material intended to protect against radiation damage, such as lead. The most intense fluorescence energies may be produced at 75 keV and several times weaker energies may be produced at 85 keV energy.
In addition, some of the high energy external radiation, once it has entered the DDA, can be scattered by materials inside the DDA, especially by light-element materials such as circuit boards. In some instances, the scattering angles can be so large as to reverse the direction of a photon, generating backscattered radiation that can impinge on other critical internal components, such as the scintillator and light imager or photodiode array. Backscattered photon intensity depends on the physics of the backscatter mechanism. At industrial inspection energies, Compton scattering dominates and light elements, such as carbon and aluminum, Compton can scatter efficiently, with the highest substantial scattering intensities backscatter direction being 180° with respect to the incident beam direction. If this radiation is sufficiently intense and prolonged, significant radiation damage can occur to the light imager and scintillator, shortening the lifetime of the DDA.
In some industrial applications, the thickness of the radiation shield that may be necessary to protect against the direct beam from the radiation source is so large that the DDA becomes prohibitively heavy. Because of safety concerns, industrial design requires that a DDA weigh near or below 100 pounds.